The Common Gateway Interface (CGI) is a simple protocol for passing an HTTP
request from a web server to a standalone program, and returning the output
to the web browser. Basically, a CGI program is
called with the parameters of the request passed in either in the
environment (GET) or via $stdin (POST), and everything it prints to $stdout
is returned to the client.

This file holds the CGI class. This class provides
functionality for retrieving HTTP request parameters, managing cookies, and
generating HTML output. See the class documentation for more details and
examples of use.

The file cgi/session.rb provides session management functionality; see that
file for more details.